Increased attention has been directed recently to the preparation of polymerizable ultraviolet stabilizers, and many classical ultraviolet absorbing groups have been made into polymerizable ultraviolet stabilizers. However, derivatives of 2(2-hydroxyphenyl)2H-benzotriazoles seem to have the greatest utility because of the superior efficiency of 2(2-hydroxyphenyl)2H-benzotriazole as an ultraviolet absorbing group.
Attention has been focused on the synthesis of polymerizable ultraviolet stabilizers of the 2(2-hydroxyphenyl)-2H-benzotriazole family which are styrene derivatives--that is, compounds where a polymerizable vinyl group is attached directly to the phenyl ring of the 2(2-hydroxyphenyl)2H-benzotriazole system.
Recently, the synthesis of several benzotriazoles has been reported, specifically 2(2-hydroxy-5-vinylphenyl)2H-benzotriazole and 2(2-hydroxy-5-methylphenyl)5-vinyl-2H-benzotriazole. Polymer Preprints, ACS Division of Polymer Chemistry, 21(1), 201 (1980), S. Yoshida and O. Vogl,; Rev. Roum. de Chemie, O. Vogl and S. Yoshida, 25(7), 1128 (1980); Makromol. Chem., S. Yoshida and O. Vogl, 183, 259 (1982); J. Polym. Sci., Polymer Chem. Ed., S. Yoshida, et al. This work has resulted in the synthesis of polymeric, non-volatile and non-leachable ultraviolet stabilizers, and was part of a general effort to produce 2(2-hydroxyphenyl)2H-benzotriazole type ultraviolet stabilizers of high molecular weight.
Other work to increase the molecular weight of benzotriazole compounds has led to the synthesis of 4[[(2H-benzotriazole-2-yl)2,6-dimethylphenoxy]methyl]benzylidene malononitrile which has also been reported to be an effective ultraviolet stabilizer, in U.S. Pat. No. 4,070,337 (1980).
The introduction of polymerizable vinyl groups into ultraviolet absorbing molecules can be accomplished in several ways. Previous attempts to introduce vinyl groups into aromatic systems were made by brominating ethyl substituents with N-bromosuccinimide and subsequently dehydrobrominating the 1-bromoethyl compound to the vinyl compound.
Another technique has been reported for the synthesis of methyl 5-vinylsalicylate by reducing the acetyl compound with sodium borohydride followed by dehydration of the 1-hydroxyethyl compound with potassium hydrogen sulfate. However attempts to introduce an acetyl group into the 2(2-hydroxyphenyl)2H-benzotriazole system to accomplish a simple and direct synthesis of polymerizable vinyl 2(2-hydroxyphenyl)2H-benzotriazole were unsuccessful.
Because of the growing importance of, and interest in ultraviolet stabilizers, much work has continued in order to develop viable syntheses for such compounds.